1. Field of the Invention
The invention relates to an image forming apparatus.
2. Related Background Art
Conventionally, in an image forming apparatus, for example, a printing apparatus with electrophotography, copying apparatus or facsimile apparatus, in order to form an image, first an electrostatic latent image is formed on a photoconductor drum by using an electrifying device to electrify the surface of the photoconductor drum and using a LED (Light Emitting Diode) head to expose the surface of the photoconductor drum. Then a toner image is formed by using an image developing device made up of a blade and a developing roller and the like to develop the electrostatic latent image. The toner image is transferred on a recording medium, for example, a sheet or film by using a transference device. An image is formed by using a fixing device to fix the toner image transferred on the recording medium.
FIG. 2 is a drawing showing the main part of a conventional image forming apparatus.
In FIG. 2, 11 is a photoconductor drum set rotating-freely along an arrow direction, 12 is an electrifying device to electrify uniformly and equally the photoconductor drum 11. The electrifying device 12 comprises an electrifying roller 13 which contacts with the photoconductor drum 11 and is set rotating-freely, and a power unit 14 supplies a surface electric potential of −700V to the electrifying roller 13.
Further, 15 is a cleaning device for removing the toner (hereinafter: residual toner) remaining on the surface of the photoconductor drum 11. The cleaning device 15 comprises a cleaning blade 16 formed from an elastic material, for example, urethane rubber, and a bracket 17 for supporting the cleaning blade 16. The cleaning blade 16 has a JIS hardness of 60 degrees, a thickness of 2.0 mm, and a projecting portion with a length of 9.5 mm, projecting from the tip of the bracket 17. Further, the cleaning blade 16 has a slant angle H (53.4°) with respect to a line extending from the center of the photoconductor drum 11 along the radial direction and is pressed with a predetermined pressure by the photoconductor drum 11. Thus, while the photoconductor drum 11 rotates, the residual toner is scraped away by the cleaning device 15. Moreover, the photoconductor drum 11, the electrifying device 12 and the cleaning device 15 construct the image forming apparatus.
When the image forming apparatus starts to be used, in order to prevent the tip of the cleaning blade 16 from being rolled up, the toner with insulation efficiency is previously smeared on the tip of the cleaning blade 16. Thus, the early torque of the photoconductor drum 11 becomes small.
However, because the electrifying device 12 and the cleaning device 15 are set in the conventional image forming apparatus, the image forming apparatus becomes big.
Therefore, a cleaning blade which has an electrifying function for electrifying the surface of a photoconductor drum and a cleaning function for removing residual toner is provided (refer to the Japanese Patent Publication No. 6-130778).
FIG. 3 is a drawing showing the main part of a conventional image forming apparatus.
In FIG. 3, 11 is a photoconductor drum set rotating-freely along an arrow direction, and 21 is an electrifying/cleaning device for electrifying uniformly and equally the photoconductor drum 11, while removing residual toner after transferring. The electrifying/cleaning device 21 comprises a cleaning blade 22 with semi-conductivity, a bracket 23 for supporting the cleaning blade 22, and a power unit 24 supplying a predetermined voltage to the cleaning blade 22 so that the photoconductor drum 11 has a predetermined surface electric potential.
The cleaning blade 22 is formed by mixing conductive particles, for example, carbon black into urethane rubber serving as an elastic material, and has a cubic resistance of 106-109 (Ω·cm).
However, in other conventional image forming apparatus, when performing printing continually, the edge portion of the cleaning blade 22 is worn away so as to become nicked. Thereby, it is impossible to keep a cleaning function. This is because the hardness of the rubber drops so that the durability of the cleaning blade 22 is gone.